"The first three articles comprehend in general terms the whole of a Declaration of Rights," said Tom Paine of revolutionary France's Declaration of the Rights of Man, and that remark applies as much to the UDHR as to the historic document Paine had in mind. In both cases the first three articles are, still to use Paine's words, "the base of liberty, as well individual as national; nor can any country be called free whose government does not take its beginning from the principles they contain."

In the UDHR those principles are that every human individual is born free and equal; that there is no basis for discrimination, on any ground of race, sex, language, opinion and more, to deprive individuals of the rights attributed to them in the Declaration; and that all individuals have the right to life, liberty and security of person.

The first thing a sceptic might say is, "Who says? On what grounds are these attributions made?" The second thing he might say is, "What do these vaporous generalities anyway mean?" And the third is, "Suppose you can answer the first two questions satisfactorily, where are the big guns to enforce them?"

Take for example Article 3. At first appearance it seems to cram too much in: "life, liberty and security of person" is a portmanteau phrase, its clarity and generality inversely proportional when compared to Article 2 of the European Convention of Human Rights, which is only about a right to life, and slightly more specific about what the right to life means – namely, that no one shall be deprived of life "intentionally" (except, it questionably goes on to say, under a capital sentence provided by law; curiously, it forgets to license also death through military action by an appointed soldiery).

But there are two resources for clarification of Article 3 and its two predecessors: the preamble and the other articles of the UDHR itself, together with the immediate background to its drafting. The drafting occurred in the years immediately following 1945; so in saying, as the preamble's second paragraph does, "Whereas disregard and contempt for human rights have resulted in barbarous acts which have outraged the conscience of mankind …" the intention of the first three articles becomes crystal clear. In the light of the Holocaust and other atrocities of war, that intention is to assert, as the default position, a status of inviolability for the human individual, independently of any other fact about him or her. For a central example, it opposes forcing him onto a train, transporting him to a death camp, and murdering him in a gas chamber there. And as a corollary it implies that there has to be a very good reason indeed for the life, the equality, the liberty or the security of individuals to be abrogated, a reason that will override those rights in the light of some more powerful consideration – such as, for example, their forfeiture by a sufficiently serious criminal act justifying deprivation of an individual's liberty.

The effect of the articles is to prise open a space, and then to protect it, in which individuals can exercise choices and capacities to make the best of their other circumstances – although here too the UDHR is ambitious and stipulative, claiming that education and decently remunerated employment are also rights.

Obviously enough the aim of the first three articles is to erect a presumption of rights as a stockade around individuals to shield them from arbitrary depredation. It is to guard them against becoming prey to the unscrupulous and the more powerful, against hostile majorities, and against tyrannical government. To the sceptic who asks, "Who says that individuals have these rights?" the argument of experience about the minimum required for a chance of human flourishing, and the vividly recent history of circumstances in which millions were regarded as not having any such rights, is a definitive reply.

The UDHR was devised as an exhortatory document, a statement of aspirations; its preamble says that it is a proclamation of "a common standard of achievement for all peoples and all nations", and enjoins UN members states and their citizens to "strive … to promote respect" for them. So although the emphatic rhetoric of the articles makes them sound legalistic and marmoreal, their force is primarily moral. That does not by one jot make them less important. They express an attitude and a determination, and pave the way for the two UN covenants, respectively on civil and political rights and on social and economic rights, that followed them.

Whatever one thinks about the wording of the first three articles, it is hard to gainsay what they aspire to lay down as minimum conditions for a human life worth the name. Nothing less than them could possibly do.

AC Grayling will continue with a daily blog on the UDHR through to the 60th anniversary itself on December 10.The Guardian is the media partner for The Convention on ModernLiberty, taking place on Saturday February 28 2009, which will debate these and other issues. You can buy tickets here